a. Field of the Invention
The invention relates to solid state devices and more particularly to a method for making fuse useful in integrated circuit construction.
B. Prior Art
Proliferation of semiconductor programmable read-only memories (PROMs), utilizing integrated circuit technology, has led to the use of PROMs in a large number of diverse applications including control of integrated circuit microprocessors, character generation, code conversion, table look-up, arithmetic logic and other control functions. In the prior art, one method of programming PROMs is by means of a fusable link which connects memory cells to reading logic. The following U.S. patents all show fuse links of the prior art: U.S. Pat. Nos. 3,564,354; 3,619,725; 3,699,395; 3,699,403; 3,733,690; 3,742,592; 3,792,319; and 3,848,238.
In prior art fuses, the fuse material has often been polycrystalline silicon or nichrome. A problem with polycrystalline silicon is that it requires a relatively large fusing current, while the problem with nichrome is one of reliability, i.e. after blowing a nichrome fuse, molten nichrome may reform, making a current path between regions where the fuse was blown. These, as well as other problems with other prior art fuses led me to search for new fuse materials.
In my prior work, I had utilized platinum in the metallization scheme for making interconnections in the formation of integrated circuits. Indeed, several U.S. patents teach the use of platinum silicide in the metallization and contact plan for the construction of integrated circuit devices, including Schottky diodes. These patents include U.S. Pat. Nos. 3,261,075; 3,426,252; 3,449,825; 3,753,807; 3,540,010; 3,558,366.
Because of the problems with prior art fuse materials, it was the object of this invention to devise a fusable link for integrated circuit construction which had greater reliability than nichrome fuses of the prior art, and had lower fusing current than polycrystalline silicon fuses of the prior art and could be manufactured in the same processing step as other integrated circuit devices or portions thereof.